OK one of my cory's is acting lethargic. The other one swims all over and is busy. This afternoon at around 4pm my husband noticed that he was sitting at the bottom of the tank in a corner and not moving but still breathing. So I tested the parameters and here are the results:
Ammonia: 0ppm
Nitrite:0ppm
Nitrate: 10ppm
pH: 7,8
Tank temp is at 78*
I did do a 50% w/c yesterday just b/c I had added fish and hadn't yet changed the water. I added the cory's on 3/4 and they have been doing fine. Then I added 5 rasboras on 3/6 and everything has been fine. The betta has been in there since 2/27 and they all get along great. What do I do? Is that normal for a cory to sit there and not really move? He had been moving all around. Also should they be going to the top of the water for breaths occasionally?? Not often but sometimes I mean. Any help would be great.
Thanks,
Paisley

How long are your cory's lethargic for?? Is an 8hr period a normal amt. of lethargy? Are the water parameters OK for him? I just checked again and the temp is at 77* (I lowered it a little since he was acting different) and he is still just sitting by a plant.? Is there anything else I should check?
P

He is moving about now pretty normalish. However, after close inspection I have noticed that his underside and gills seem more pink than the other cory?? He also seems to spin/tip a little on purpose while swimming, like soemthing is bugging him and he's trying to get it off. I will test the bottom of the tank water as you suggested and get back to you in a few hours. We have a birthday party to go to so it might be after that. I am very concerned now that I notice him tipping while swimming, I was happy he is moving about though. I am not going to feed them today just in case.
P

Okay I tested the bottom water in the tank and it was fine:
Ammonia: 0ppm
Nitrite: 0ppm
Should I also test the bottom water pH and Nitrate, would they vary down there also??
While watching a few minuets ago the cory was acting normal. Busy scavenging on the plant leaves and all of the sudden the betta came over and bumped him in the face!!! Then the cory went to the bottom and the betta went after him a little...he wasn't flaring or anything but it looked almost like the betta was trying to nip his top fin!! So immediately I grabed the fish net and got the betta out of the way. I just filled the 'death cube' and put the betta in there temporarily. I am wondering if maybe this was going on but only when I wasn't watching or at night? I do sit and stare at the fish often so I find it strange that I have never seen this behavior before. Would the betta be able to tell that the cory doesn't feel well and then start harassing him? Or do you think that maybe this is the cause for the cory acting funny etc.? Either way I have got to decide what to do quickly.
It seems that my only options would be to see if the LFS will take the cory's back or to get a smaller (2.5-5gallon) betta tank. Of course, my inclination is to get the betta tank but I am POSITIVE that my husband will say NO I don't want to get rid of the cory's though, I have become really fond of them and they seem to be very interactive and friendly. They will swim right up to my hand when I am testing water or adjusting the heater etc. I am really surprised at how outgoing they are. I was figuring that they would stay near the bottom or hide since there are only 2 of them in there. They will also swim right into the betta's space sometimes like they aren't scared of him at all. It seems like they wouldn't do that if he had been harassing them but I really don't know too much. Any input would be great:)
Paisley

Okay so he is not doing so well today again yesterday I did a 30% w/c and took the betta out of the tank so that I could lower the temp a bit. 3 hours after the w/c I took water from the bottom of the tank and tested it. Nitrate: 10ppm
pH: 7.0
I was surprised at how the pH had gone from 7.8 to 7.0 with only a 30%w/c. But I thought that was good! So today the cory seemed to be almost dead at the bottom just sitting there. I was able to get him to move by touching him but was shocked that he actually let me touch him a tiny bit before he started swimming. I thought for sure he was dead. He began swimming about like normal and after about 5 min. I noticed he was swimming funny every couple of seconds like trying to spin or tip while swimming but very quickly. Almost like he had something stuck on him that he wanted off.? I did see him kind of run into the substrate like he was 'scratching' himself or something. What would that signal??
I did a 50% w/c right away but first tested the water from the bottom of the tank again at 2pm today.
Nitrate: 5ppm
Nitrite: 0ppm
pH: 7.8---->surprised that it got that high that quickly from yesterday's test at 6pm
Ammonia: 0ppm but it almost looked like "maybe" there could have been a hint of green to put it at .25ppm but only when I looked at it in a certain light or tilted it a certain way. It was questionable whether or not it was even there.
When you guys test your water do you hold the tube right up against the white background or a tiny bit away from the background?? I have noticed that when I am trying to read my pH readings that if I hold the tube and the card in one hand (right up against the background/touching it) it looks darker, but if I hold it the tinyest bit away from the white background it looks lighter.?? Has anyone else noticed this whit their testing? I use the API Master one.
Thanks,
Paisley

Once they start spinning it's very difficult to bring them back. I'm not always sure what causes it... cories are super sensitive so it could be anything from water quality to a parasite, to a bacterial or fungal infection, to them getting a face full of anaerobic gas from a pocket in the substrate. Simple shock (quick temp or pH change) can also cause it.

It sounds like your water needs to sit straight out of the tap before it reaches its true pH. You may want to consider using "aged" water (water that's sat at least 24 hours) in water changes. With small tanks, it's not terribly difficult.

My pH is right around 7.8 out of the tap and the only corydoras I've had trouble with are wilds and habrosus (dwarf cories)._________________Dumpster TankNano FishMbuna